Traveling Ionospheric Disturbances (TIDs) are an important Space Weather effect in the upper atmosphere constituting a threat for operational systems using predictable ionospheric characteristics. TIDs can impose disturbances with amplitudes of up to ~20% of the ambient electron density, and a Doppler frequency shifts of the order of 0.5 Hz on HF signals. It is clearly demonstrated that TIDs can have multiple effects in the operation of aerospatial and ground-based infrastructures and especially in the European Geostationary Navigation Overlay Service (EGNOS) and Network Real-Time Kinematic (N-RTK) services, in High Frequency (HF) communications, in radio reconnaissance operations and in Very High Frequency – Ultra High Frequency (VHF-UHF) radiowave propagation.
The TechTIDE-HORIZON 2020 project aims at delivering in real-time data, products and services capable of detecting the occurrence of TIDs over specific regions. Furthermore, in close collaboration with operators of the technologies concerned, TechTIDE consortium will design and test new viable TID impact mitigation strategies and will demonstrate the added value of the proposed mitigation techniques which are based on TechTIDE products.
In this contribution we present first results from the TID detection methodologies that are based on the analysis of Digisonde, GNSS and Doppler Sounding data using complementary modeling techniques for Medium Scale and Large Scale TID identification. More precisely we apply the following methodologies:
1. HF-TID, based on Digisonde to Digisonde operations. The method detects quasi-periodic oscillations that the HF signal exhibits as it propagates a trans-ionospheric channel that is modulated by TID perturbations;
2. HF Interferometry, that identifies LSTIDs for a network of Ionosondes. It detects quasi-periodic oscillations of ionospheric characteristics and identifies coherent oscillation activity;
3. Spatial and Temporal analysis of GNSS measurements, that allows the detection and characterization of MSTIDs and LSTIDs, including velocity and period;
4. TEC gradients, that detecs LSTIDs occurring during geomagnetic storms. In such conditions, strong temporal and spatial TEC gradients are observed closest to the source region of LSTIDs;
5. The 3D EDD method, based on the reconstruction of the 3D electron density distribution (EDD), developed on the basis of the Topside Sounding Model-assisted Digisonde (TaD) profiler. It ingests Digisondes and GNSS data and it is sensitive to LSTIDs;
6. The CDSS – multipoint Continuous Doppler Sounding System (CDSS) method is able to detect fluctuations of the Doppler shift of the transmitted frequencies caused by the TIDs passing over reflection point and to estimate MSTIDs characteristics.
The analysis focuses primarily on periods of enhanced auroral activity. TechTIDE identifies perturbations in the amplitude of the electron density and on the HF propagation characteristics (azimuth, elevation, Doppler shift). For the evaluation of results, we are using data from the geospace and the lower atmosphere. The AATR (Along Track TEC Rate) parameter, is used in the validation plan as an indicator for the TIDs at different latitudes.

ESA’s Galileo Science Office (GSO) is coordinating ESA GNSS scientific related activities in a close cooperation between the Navigation and Science Directorates. These activities are focussed in the use of the GNSS/Galileo programmes for research in Earth Observation, navigational and physical sciences. In this context it is of great interest for the Office to evaluate the performances of GNSS/Galileo Technologies in extreme environments.

In this respect, an opportunity was offered to colaborate with the 'Antarctica Unexplored' expedition, mounted by Spain's Asociación Polar Trineo de Viento for the Southern Summer season 2018-2019. This expedition was based in the use as a scientific platform of a well proven Windsled specially designed for polar regions. It allowed great mobility and access to remote places that currently require complex and expensive access for research. This expedition carried a total of 10 scientific experiments from different research institutions, covering fields such as climate change, meteorology and astrobiology.

ESA's involvement with the expedition was the Galileo Experimentation and Scientific Test in Antarctica (GESTA) project. The objective of this activity was to evaluate the performances of GNSS/Galileo Technologies in extreme environments like the Antarctic Plateau. This analysis aimed to study in such environment the GNSS HW performance and operation, GNSS performances in high latitudes and specific scientific applications in polar regions. GSO provided training and equipment to the expedition members to carry out and operate ESA GNSS/Galileo Equipment to obtain GNSS measurements in different times, locations (variable latitude and altitude) and situations (diverse geomagnetic and meteorological conditions). The expedition team kept in continuous contact via satellite with GSO, allowing to plan their activity during space weather relevant events.

Finally, the expedition travelled 2500 km in 52 days arriving to a Southern geographical latitude of 79°38'14.38"S. During the expedition 174 hours of GNSS data were captured. At the moment, the following analysis/evaluations are being performed with the captured data:

* HW Performance Evaluation;
-Reception performances of a Multiconstellation and Multiband GNSS receiver,
-Evaluation of HW performances in Antarctica,

* Galileo Navigation Performances;
-Evaluation of the PVT precision in high latitudes of the different GNSS,

* Scientific Applications;
- Ionosphere Characterisation at High latitudes,
- Ionospheric Scintillation and other propagation issues during Solar activity.

The paper will presents in detail both the expedition and the results of the performed analysis

This presentation will summarize the main contributions of the ESA-funded projects PIOM-FIPP, HORION and ATOMIC to the research on ionospheric modelling and its impact on precise GNSS processing, and the corresponding transfer to the Industry. Indeed, the two first activities were able to provide, respectively:

1) A new simple technique to mitigate in relative GNSS precise positioning the predominant effect of frequent ionospheric waves (MSTID). This is the so called direct GNSS Ionospheric Interferometry technique (dGII). The dGII details including, the impact on precise GNSS processing were summarized in Hernández-Pajares et al. (2017).

2) A full implementation of the four main higher order ionospheric corrections for GNSS raw measurements, the second- and third-order, the geometric- and differential STEC-bending terms, was implemented, characterized and transferred to the industry, in form of a web-based service for very precise GNSS processing (see Hadasz et al. 2017).

Moreover the project ATOMIC is finishing during 2019 in order to approach to the industry the Wide Area RTK technique for precise relative GNSS positioning (Hernández-Pajares et al 2003, 2007).

References:

Hadas, T., Krypiak‐Gregorczyk, A., Hernández‐Pajares, M., Kaplon, J., Paziewski, J., Wielgosz, P., Garcia-Rigo, A., Kazmierski, K., Sosnica, K., Kwasniak, D., Sierny, J., Bosy, J.,Pucilowski, M., Szyszko, R., Portasiak, K., Olivares-Pulido, G., Gulyaeva, T., and Orus-Perez, R. (2017). Impact and implementation of higher‐Order ionospheric effects on precise GNSS applications. Journal of Geophysical Research: Solid Earth, 122(11), 9420-9436.

Hernández-Pajares, M., Zomoza, J. M. J., Subirana, J. S., & Colombo, O. L. (2003). Feasibility of wide-area subdecimeter navigation with GALILEO and modernized GPS. IEEE Transactions on Geoscience and Remote Sensing, 41(9), 2128-2131.

Hernández-Pajares, M., Juan-Zornoza, J. M., Sanz-Subirana, J., & Garcia-Rodriguez, A. (2007). U.S. Patent No. 7,256,730. Washington, DC: U.S. Patent and Trademark Office.

Hernández‐Pajares, M., Wielgosz, P., Paziewski, J., Krypiak‐Gregorczyk, A., Krukowska, M., Stepniak, K., Kaplon, J., Hadas, T., Sosnica, K., Bosy, J., Orus-Perez, R., Monte-Moreno, E., Yang, H., Garcia-Rigo, A. and Olivares-Pulido, G. (2017). Direct MSTID mitigation in precise GPS processing. Radio Science, 52(3), 321-337.

The magnetic storm of September 6 to 10, 2017 was caused by an X9 solar flare followed by a Coronal Mass Ejection (CME). The storm sudden commencement (SSC) occurred around 24 UT on the night of 06/07 due to a sudden increase in solar wind from 400 km/s to about 600 km/s. Ionospheric scintillation was measured by the AFRL/VHF receiver at São Luís and several GNSS receivers located in Brazil. Considering that scintillation may affect the GNSS signals and consequently the navigation and positioning systems, it is very important to analyze its behavior during such storms. In this contribution the aim is to analyze the effects of this magnetic storm on the quality of precise point positioning (PPP) in several stations over Brazil. GNSS data from several stations was processed using the kinematic PPP approach. Preliminary results provided evidence that the effects were at minimum level. A detailed analysis will be presented considering ambiguity resolution, residuals and position accuracy.

Higher order ionospheric effects, which can not be eliminated through a combination of dual-frequency GNSS observables, can be significant for high precision positioning applications during geomagnetic storm periods, especially satellite orbit and clock estimation from global GNSS network data. The largest part of higher order effects, the 2nd order, is estimated using slant total electron content (TEC) and modeled geomagnetic field components at the ionospheric pierce points. Estimation errors of the slant TEC and modeling errors of the geomagnetic field can induce large errors during severe space weather conditions.
There have been a number of studies on the characteristics of higher order ionospheric effects. Although insignificant during low solar activity periods, their effects are systematic with respect to Earth’s North and South hemispheres. A few studies have also shown the impact on high precision positioning applications. At the Canadian Geodetic Survey of NRCan, higher order effects are regularly estimated and monitored at ionospheric pierce points observed by more than 350 globally distributed GNSS stations. They are also accounted for in its GNSS satellite orbit and clock products generation. In this presentation, impacts of higher order effects on satellite orbit and clock estimation are analyzed during geomagnetic storm periods.